70 DUBLIN NATURAL HISTOKY SOCIETr. 



a generative act, until in its turn, by another generative act, it assists to 

 give rise to a new germ, be observed — just as an oak is known to pro- 

 duce an acorn, which acorn will by-and-by produce another acorn-bear- 

 ing oak — it cannot be affirmed that any given organism is in reality a 

 true species. That is, it is not proved that some allied form, which in 

 the present state of knowledge we are constrained to suppose a distinct 

 species, may not in truth be only a phase of variation, or of develop- 

 ment, or an alternation of generation of the actual species, whose extremes 

 of variation, or whose life history, are as yet unknown, 'Now, in the 

 family of Algse, to which I have the pleasure to-night to make a small 

 addition (the Desmidiacese), this whole course of development has not 

 been traced, except in two or tliree instances, and in many species even the 

 characteristic form of the sporangium following conjugation, which here 

 represents the reproductive condition, is unknown, although frequently 

 met with in other species. But even in regard to the numerous Desmi- 

 dian species which have not been so traced up to the development of new 

 individuals, but only so far as the conjugative act itself, and the forma- 

 tion and perfecting of the resultant sporangium (frequently, indeed, met 

 with), I would draw attention to a circumstance I am disposed to look 

 upon as an almost unimpeachable argument as to their actual specific 

 distinctness. I allude to the fact, that, no matter how numerous or how 

 few the fronds, the conjugating specimens always conjugate, like form 

 or species with like form or species — the abundant with their abundant 

 neighbours of the same species, the rare seeking out the rare of the same, 

 overlooking species, and the possibly more numerous specimens of a per- 

 haps closely allied species. And it is marvellous, however few a certain 

 species may be amongst the mass of others, by what attraction or force 

 these little vegetable organisms, not endowed with a locomotive power, 

 are impelled to seek only their fellows when about to conjugate, avoid- 

 ing other more abundant species, themselves even, perhaps, conjugating 

 with each other at the time. The same may be said to be true of other 

 Conjugatce. Such at least is my own experience ; yet, at the same time, 

 that a hyhrid might occur amongst the lower Algse, as well as amongst 

 higher organisms, is perhaps not impossible ; but even if it did, it does 

 not appear to me that such a circumstance would weigh as an argument 

 against the existence of actual species in this family. But, further, I 

 believe if the development from one generative act to another has been 

 traced in a few, even in one species, and the result of such investigations 

 has been to prove that the so observed parent form or species, after pass- 

 ing thi'ough its reproductive stages, gives birth to its own complete 

 likeness, that its specific rank has to all intents and purposes been es- 

 tablished. I^ow this has been done by Professor de Bary in regard to 

 at least two species of Cosmarium, C.Botrytis and C. Meneghinii ; and it 

 is worthy of remark that these are both forms whose specific distinctness 

 has been called in question by some observers, merely because they con- 

 siderably resemble certain allied species of Cosmarium. To my mind, 

 indeed, they seem, in a word, to possess only common generic characters; 

 and for my share, while both the above species are frequent, I believe 



